1. Field of the Invention
The present invention relates to a solid fuel burner and furnace construction. 2. Description of the Prior Art
In the prior art, various furnace constructions having been advanced for burning solid fuel, including coal. Many have also used stepped burner grates, but the problems with complex drives, complex mounting, and inadequate movement of the grates have continued to limit their success. For example, in the prior art, a typical stoker-actuated coal burning apparatus is shown in U.S. Pat. No. 4,007,697 which utilizes a furnace cabinet having a burner with a rotating disk thereon. This shows a heat exchanger that provides for a curved path for the heated products of combustion and a separate burner blower.
U.S. Pat. No. 945,469 issued to Mapel on Jan. 4, 1910 shows a stepped grate in an automatic stoker apparatus wherein the grate assembly is mounted on wheels that can be moved in and out of the furnace, and includes a crank mechanism which has a double-acting lever arrangement to reciprocate the adjacent stepped grates in opposite direction when the crank rotates. However, the drive requires a complex lever system and the grate plates themselves are supported only on the lever arrangement, thus increasing wear on the actuating members, and tending to cause jamming and excessive loads in the heated, ash-filled environment in which the grates must work.
U.S. Pat. No. 1,644,953 issued to Seyboth on Oct. 11, 1927 is typical of a number of patents in the prior art which show a stepped grate where every other grate plate is fixed, and then the intermediate plates or bars forming the steps are driven to reciprocate. Very complex gear drives are utilized, and the grates are separated into sections for movement, resulting in the need for a large number of links, bell cranks, and levers.
U.S. Pat. No. 505,748 issued to Campbell on Sept. 26, 1893 shows a grate assembly that has a plurality of bars that are mounted on side plates and which interfit between stationary bars and reciprocate as a unit. The unit is mounted on roller-type bearings, and all of the movable grate bars thus reciprocate as a unit relative to the interfitting stationary bars.
U.S. Pat. No. 2,137,158 to Douglass issued Nov. 15, 1938 shows a "clinker cooling" arrangement using stepped grates and having reciprocating step members with a cooling fluid going through the plates. Every other grate bar is fixed. The unit is used primarily for cooling Portland cement clinkers.
U.S. Pat. No. 795,388 issued to Googins on July 25, 1905 shows a reciprocating terraced furnace grate, and in particular in FIGS. 9 and 11, the end edges of the grates are shown to be tapered. However, the grate bars also appear to be supported on lower rollers of car-type structures so that the grate bars on one of the cars interfit or interleaf with the grate bars of the other car, and then they are oscillated in opposite directions as they are used. The grate bar surfaces incline slightly downwardly.
U.S. Pat. No. 4,103,627 to Mainka issued Aug. 1, 1978 shows a grate construction which has reciprocal grate members made up into individual sections that are pivotally mounted to their supporting members. Some of the grate bars reciprocate relative to other grate bars.
The use of holes or openings through burner grates is also shown in the prior art, for example, U.S. Pat. No. 2,137,158 mentioned above, illustrates holes in the grates, but tapered in opposite direction from those disclosed in the present application. U.S. Pat. No. 1,403,609 issued to Leonard et al on Jan. 17, 1922 also shows reciprocating grates with tapered holes, but which are mounted in a substantially different manner than the present device. The grates in U.S. Pat. No. 1,403,609 do not reciprocate although pusher members are provided between the vertically spaced grates. U.S. Pat. No. 703,068 issued to King on June 24, 1902 illustrates a mechanism for driving sliding grate members from a type of a feed auger, as does U.S. Pat. No. 2,119,937 issued to Banfield on June 7, 1938. In the Banfield Patent a rotating grate is driven from the stoker auger.
U.S. Pat. No. 527,453 issued to Richards on Oct. 16, 1894 shows a traveling floor furnace where there are elongated grate members which move, and which are inclined rather than stepped.
U.S. Pat. No. 804,457 issued to Cox on Nov. 14, 1905 shows an ash conveyor for furnaces which uses reciprocating stepped members, and U.S. Pat. No. 1,186,971 issued to Davis on June 13, 1916 shows a grate member that has plates that tilt under mechanical action to move materials.
U.S. Pat. No. 2,294,269 issued to Bennett on Aug. 25, 1942 shows a stepped, movable, water-cooled stoker having plates that slide relative to support shelves, but designed to include the water cooling for absorbing heat quickly.
U.S. Pat. No. 4,172,425 issued to Sheridan on Oct. 30, 1979 shows an incinerator that has movable members for transferring waste through the incinerator, but not a stepped grate construction such as the present invention, and U.S. Pat. No. 3,413,938 issued to Dvirka on Dec. 3, 1968 shows another form of a stepped grate member where the material is primarily moved by pushing grates against the material to cause it to move downwardly as it is burned.
The prior art, while showing a wide variety of stepped grates and furnace constructions, fails to teach or suggest a unit arranged with the stepped grate construction of the present invention in a furnace cabinet that provides for a high efficiency of air flow and heat exchange.